An orthogonal frequency division multiplex access (referred to as OFDMA or OFDM-FDMA) scheme is one of multiple access schemes. In the OFDMA scheme, a base station forms one service cell and allocates at least one of subcarriers, which are different from each other, to at least one mobile station included in the service cell. Accordingly, the OFDMA communication system can minimize interference in the cell.
In the OFDMA scheme, the mobile station transmits signals in uplink with restricted power. Therefore, when the mobile station is located at the edge of a cell, the mobile station cannot transmit packets in uplink because of a lack of sufficient power. For this reason, in order for the base station to properly receive packets from the mobile station located in the service cell, it is necessary to restrict interference generated from an adjacent cell to be less than a specific level.
In a mobile communication system of a general OFDMA scheme, when the mobile station is located in a cell, path loss between the mobile station and the service cell is smaller than that between the mobile station and an adjacent cell. In this case, the mobile station experiences little restriction on transmission power and transmits packets using comparatively high power in the uplink.
However, when the mobile station is located at the edge of a cell, since the mobile station is close to an adjacent cell, interference by the adjacent cell due to the transmission power of the mobile station can occur. Therefore, the mobile station reduces the amount of uplink interference power that interacts with the adjacent cell by restricting the transmission power, and transmits the packets by using a comparatively low power in the uplink. However, the mobile station requires recognition of an interference situation of the adjacent cell so as to control the transmission power.
Thus, according to the mobile communication system of the general OFDMA scheme, the interference influence of the cell is divided into three stages, and the base station broadcasts the interference stage of the service cell into the stage of a mobile station located in the service cell and an adjacent cell with a very low encoding rate over a specific broadcasting channel (OSICH). The mobile station receives the interference stage of the adjacent cell through the specified broadcasting channel (OSICH), and controls the transmission power in consideration of the interference stage of the adjacent cell.
As described above, according to the mobile communication system of the general OFDMA scheme, the base station transmits the interference stage of the service cell with a 2 bit OSI value such that the mobile station can control the transmission power according to the interference stage of the adjacent cell. For this reason, since only some mobile stations are capable of receiving the OSI value and can recognize the interference stage of the adjacent cell, it is difficult for the control of transmission power to be commonly applied to all mobile stations that bring about the interference of the adjacent cell. In addition, the mobile station should periodically receive the OSI value corresponding to the interference stage of the adjacent cell from the base station of the adjacent cell so as to recognize the interference stage of the adjacent cell.
Since the base station utilizes one OFDM (orthogonal frequency division multiplex) symbol so as to transmit the 2 bit OSI value corresponding to the interference of the service cell, radio resources can be unnecessarily wasted.
Moreover, the mobile station sets the transmission power in consideration of the interference stage of the adjacent cell and sets the transmission power by using a power control report message. In order to inform the base station of the set transmission power, the mobile station should carry out processes such as, for example, an uplink band request for the transmission power report message, band allocation through a control channel, and transmission of the power control report message. Accordingly, the mobile station cannot quickly report the transmission power to the base station. When the base station is not able to receive the power control report message from the mobile station, the base station carries out uplink scheduling by using incorrect information. Accordingly, there is a problem in that the reception success rate of an uplink traffic burst is decreased.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.